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LM5116 Layout

Michal Dudka
Prodigy 110 points
Other Parts Discussed in Thread: LM5088, LM5116

Hi

i am bulding solar regulator with lm5116 (previous version with lm5088 works well, but i dont want to cool diode) . First i've tested this lm5116 layout with 1 Ohm load at 6V, and converter oscillated with frequency around 1.8kHz (there was periodic intervals, when regulator was "stopped"). With output voltage below 4.5V was stable. Next i've try charge 12V battery, from 30V power source, and some time it works properly. Probably i've accidentaly bring higher voltage from output to FB pin and lm5116 don't work now (draws ~30mA, heating itself,  and hold high FET closed).

Can anybody please look  for potential mistakes in my layout (i didnt find reason of oscillations) or give me some suggestions how to improve it ? 

Thanks
Michal

Snubber components and transistor at feedback network are not mounted:
 
 

  • 0
    Mastermind 7395 points

    The GND connection from Cout to the device is not looking so good, it is a long and thin conductor. I didnt understand why the PNP at the output. The Vin connection could also be made a lit better, wider, close to the device.

    But I couldnt say that any of this explains the oscillations.

    Best regards, 

    Avi

  • 0 in reply to Avi Chami1
    Prodigy 110 points

    Thanks, i will redesign these two traces and try it again. PNP should be used for control output voltage. 

    Michal 

  • 0 in reply to Michal Dudka
    TI__Guru 59121 points

    Hi

    Please adjust the bottom feedback resistor rather than the top resistor. The resistance of the top resistor shouldn't be changed becasue it affects over all loop response.

    Also ,there is a liitle worry about  noise injection from inductor to the current sense.

    Regards,

  • 0 in reply to EricLee
    Prodigy 110 points

    Hi,

    i've moved adjustable resistor from top to feedback. Problematic oscillations (250Hz) probably were caused by switching between internal regulator VCC and external source from VCCX. I've measured sawtooth signal at VOUT with maximum at 4.5V with load resistance approximately 1 Ohm. When i moved VCCX from VOUT to GND, oscillations dissapeared. During tests i had SPD30N03 as top FET, next i've changed it to IRFR540Z. Some test vith 30V VIN looks good, but when i've set VIN at 45V, chip stop working, draws ~30mA,  VOUT ~ 0V, no signals at HO, very low signal at LO and internal regulator provides VCC only ~4.4V with following waveform:

     

    Have anybody idea, what i've done wrong ?

    Thanks
    Michal Dudka 

  • 0 in reply to Michal Dudka
    TI__Guru 59121 points

    Hi

    Something is damaged I think. Please look at Cvcc or any aother components connected to VCC are damaged or not.

    Regards,